I'm very glad I helped you get involved!
It's a bit late, but here's my experience with prop weapons:
PAx 09 my sister and I were asked to put orange tips on our SMG and pistol for our ODST costumes. We took a piece of bright orange paper off an ad and taped it to the front using blue painter's tape (they said the blue tape would not work on its own since it wasn't an orange safety color)
PAX '10 we had zero issues with weapons. I brought along the same SMG and pistol as in '09 as well as one of Adam's ARs and one of Lee's Halo1 style pistols. The photos someone mentioned they were looking for are available for viewing at this URL until my Flickr account expires (moving over to Smugmug):
http://www.flickr.com/photos/trooper715/sets/72157624787914965/
Unfortunately this had to be the first year PAX is not held on Labor Day weekend, making it difficult for me to attend. I am currently over in North Carolina under activation orders with the Marines, and trying to convince my chain of command to give me time off is a bit of a stretch (though I'll definitely be giving it a try). Looks like you folks definitely have things organized, and I really wish I could be there. Someone needs to convince them to make this an annual event, or some of you folks need to come out next year for when Halo4 comes out.
PS Kevin, want me to give you admin access for that FB California/west coast halo group so you can try to organize things there a bit as well?
If only this was on labor day weekend so I could be sure of getting some time off!